This competing renewal application requests continuation of clinical and basic research evaluating different cochlear implant prostheses. Ninety- five postlingual profoundly deaf adults implanted with 3 different multichannel prostheses will be engaged in a within-subject clinical trial of speech processing strategies. Secondly, 45 prelingually profoundly deaf children (2-13 years of age) will be implanted with multichannel cochlear implants to determine if the age at implantation affects outcome. This collaborative effort involves five areas of investigation: audiology, psychology, aural rehabilitation, electrophysiology, and speech production. Audiologic performance will be evaluated after brief and long-term experience with either analogue or interleaved pulsatile speech processing algorithms using MiniMed and lnerald cochlear implants. Nucleus users will participate in a trial contrasting two speech processing strategies. Psychological studies will evaluate the behavioral and emotional consequences of cochlear implants in both adults and children. Psychological variables that may be predictive implant use will be assessed. The adult Aural Rehabilitation Project will determine differences between rehabilitation approaches and assess the importance of communication strategies. The relationship between intraoperative measures of cochlear nerve action potentials and performance with an implant will be explored in an electrophysiologic project. Animal studies will be used to correlate electrophysiologic measures and morphology of the peripheral auditory system. A children's aural rehabilitation and speech production project will assess the relative contribution of age and home-based rehabilitation to outcome. The overall objectives of the research program include: 1) optimize speech coding algorithms for individual subjects to reduce performance variability; 2) develop electrophysiologic and psychologic measures predictive of outcome; 3) provide long-term follow-up of multichannel implant recipients; 4) assess the impact of implant coding strategies and audiovisual training on communication functioning; 5) measure the utility for methods of enhancing performance of multichannel cochlear implants in prelingually deafened children and determine the effect of age at implantation.